Leaves of the green tea plant camellia sinensis contain up to 36% polyphenols on a dry weight basis, however, their composition varies with climate, season, variety and state of maturity. Green tea catechins are the predominant group of green tea polyphenols. Examples of catechins are (−)-epicatechin (EC), (−)-epigallocatechin gallate (EGCG), epigallocatechin (EGC) and epicatechin gallate (ECG).
EGCG is the most interesting compound among the above mentioned catechins because it exhibits a strong antioxidant effect. Furthermore, it has been demonstrated that EGCG has an antimutagenic effect, an antibacterial effect, and a beneficial effect on cholesterol level in blood. The other catechins present in green tea are much less effective compared to EGCG. Green tea also contains other components such as caffeine, proteins, pectins, and/or metal ions which might not be desirable.
There is, therefore, a need to isolate EGCG in a pure form in high yield by a simple and economical process. However, the structural similarities of the various green tea catechins make the separation of the individual catechins difficult. Furthermore, the catechins in green tea are normally accompanied by caffeine, which is present in an amount up to 4% of the dry mass of the green tea leaves. Caffeine is known to associate with the catechins and is not trivial to remove.
The production of green tea extracts is well known in the art. Ekanayake, et al., U.S. Pat. No. 5,879,733 (“Ekanayake '733”) describes the preparation of a green tea extract having improved clarity and color. The green tea extract is obtained by treating the extract at a temperature in the range of 25° C. to 60° C. with an amount of a food grade cation exchange resin effective to remove metal cations present in the extract. The treated extract is then contacted with a nanofiltration membrane. However, the process described in Ekanayake '733 is not suitable to separate EGCG from a mixture of tea catechins.
Hara, U.S. Pat. No. 4,613,672 (“Hara '672”) describes a process for the preparation of pure EGCG which process includes the following steps: Tea leaves are extracted with hot water or with aqueous solutions of 40-75% methanol, 40-75% ethanol or 30-80% acetone. The obtained extract is washed with chloroform, and the washed extract is dissolved in an organic solvent. The organic solvent is distilled off, and the concentrated extract component is subjected to high speed liquid chromatography using a reverse-phase partition column with a developer of acetone/tetrahydrofuran/water (0-25:0-35:65-85, vol %), whereby each of (−) epicatechin, (−) epigallocatechin, (−) epicatechin gallate and (−) epigallocatechin gallate is isolated from one another. The process described in Hara '672 does not permit an economical production of EGCG on a technical scale because of the use of expensive column fillings. Furthermore, the process described in Hara '672 does not permit the production of EGCG, which may be added to food products because the solvent mixture used (i.e., acetone/tetrahydrofuran/chloroform) is not food-approved.